Chrontel
AN-118
PCB Layout and Design Considerations for CH7231
1.0 Introduction
The CH7231 is a device targeting the USB Type-C Electronically Marked Cable (E-Marker). The device is
designed to follow the USB Type-C Specification 1.1 and the USB Power Delivery Specification Revision
2.0, Version 1.1. The power delivery should support a maximum 5A current. The size of a PCB has a
limitation based on E-Marked USB cable assembly.
This application note focuses only on the basic PCB layout and design guidelines for CH7231, USB TypeC Plug and cable solder line-pads. Since the mechanical design of USB Type-C Plug and the pin sequence
of cable solder line-pads are manufactory related, guidelines in component placement, power supply
decoupling, grounding, input/output signal interface are generally discussed in this document.
The guidelines discussed here are intended to optimize the PCB layout and applications for this product.
They are only for reference. Designers are urged to implement the configurations and evaluate the
performance of the E-Marked USB cable prior to bringing the design to production.
2.0 Component Placement
Components associated with CH7231, USB Type-C Plug and cable solder line-pads should be placed as
close as possible to the respective pins. The following discussion will describe guidelines on how to
connect critical pins, component placement, and layout associated with these pins.
2.1
CH7231 placement
Since VCONN1 and VCONN2 of CH7231 are interchangeable, a flexibility of CH7231 placement is given
for PCB optimum routing according to different pin sequence of cable solder line-pads from different cable
manufactory.
2.2
Power Supply Pins and De-coupling
According to USB Type-C Cable Connection Specification, all VBUS pins shall be connected together
within the USB Type-C plug. A 10 nF capacitor (minimum voltage rating of 30V) is required for the
VBUS pins in the full – featured cable at each end of the cable. The bypass capacitor should be placed as
close as possible to the power supply pad. All VBUS pins should be connected to a VBUS power plane.
Vconn is a Type-C cable plug power. It is independent of VBUS and, unlike VBUS which can use USBPD to support higher voltage. Vconn voltage is fixed at 5V.
2.3
Ground Pins
The ground pin of CH7231, USB Type-C Plug and cable solder line-pads should be connected to a
common ground plane to provide a low impedance return path for the supply currents.
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2.4
Plug Configuration Detection Pins
CC is used for USB – PD communication. CC pin is connected through the cable to establish signal
orientation. All the CC pins from CH7231, USB Type-C Plug and cable solder line-pads should be
connected together. CC trace shall have characteristic impedance of 32 Ω to 53 Ω.
2.5
Data path of differential signal pairs
There are five pairs of USB differential signals going through the PCB board. These data paths must meet
USB Differential Pairs Impedance requirement. Additionally, routing of each pair of differential signals
must be delay matching.
D+/D- traces shall have differential characteristic impedance of 90 Ω ± 15 Ω.
The USB SuperSpeed traces should be as short as possible and have a nominal differential characteristic
impedance of 85 Ω ± 9 Ω.
The differential pairs should have a minimum pair-to pair separation of 0.5 mm.
The intra-pair skew for a differential pair is recommended to be less than 10 ps/m.
2.6
Auxiliary Signals
SBU1 and SBU2 are for sideband use. The wire shall have characteristic impedance of 32 Ω to 53 Ω.
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3.0 Reference Design Example
Figure 1 is the reference schematic of CH7231 TSOT23-5.
U1
RX1+
B11
RX1-
B10
VBUS
B9
SBU2
B8
B7
B6
VCONN2
B5
VBUS
B4
TX2-
B3
TX2+
B2
B1
GND
GND
RX1+
TX1+
RX1-
TX1-
Vb us
Vb us
SBU2
CC
Emp ty
D+
Emp ty
D-
Vconn
SBU1
Vb us
Vb us
TX2-
RX2-
TX2+
GND
RX2+
GND
A2
TX1+
A3
TX1-
A4
VBUS
A5
CC
A6
D+
A7
D-
A8
SBU1
VBUS
1
2
U4
1
2
3
Vconn 2
3
Vconn 1
5
5
NC
CC
4
GND
4
6
7
A9
VBUS
A1 0
RX2-
A1 1
RX2+
CH7231 SOT23-5
8
9
10
Vb us
19
GND
20
U2
A1
GND
B12
TX1+
TX1CC
Vb us
RX1+
RX1SBU2
18
VBUS
17
16
15
D+
DSBU1
RX2-
Vconn
TX2-
RX2+
TX2+
GND
GND
14
VCONN1
13
12
11
A1 2
Solder Lines
USB Full-Featured Type-C Plug
VBUS
C1
10 nF
Figure 1: CH7231 TSOT23-5 Reference Schematic
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4.0 Revision History
Table 1: Revisions
Revision #
1.0
4
Date
09/09/2015
Section
All
Description
Original draft
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Disclaimer
This document provides technical information for the user. Chrontel reserves the right to make changes at any time
without notice to improve and supply the best possible product and is not responsible and does not assume any
liability for misapplication or use outside the limits specified in this document. We provide no warranty for the use of
our products and assume no liability for errors contained in this document. The customer should make sure that they
have the most recent data sheet version. Customers should take appropriate action to ensure their use of the products
does not infringe upon any patents. Chrontel, Inc. respects valid patent rights of third parties and does not infringe
upon or assist others to infringe upon such rights.
Chrontel PRODUCTS ARE NOT AUTHORIZED FOR AND SHOULD NOT BE USED WITHIN LIFE SUPPORT
SYSTEMS OR NUCLEAR FACILITY APPLICATIONS WITHOUT THE SPECIFIC WRITTEN CONSENT OF
Chrontel. Life support systems are those intended to support or sustain life and whose failure to perform when used
as directed can reasonably expect to result in personal injury or death.
Chrontel
2210 O’Toole Avenue, Suite 100,
San Jose, CA 95131-1326
Tel: (408) 383-9328
Fax: (408) 383-9338
www.chrontel.com
E-mail: sales@chrontel.com
2015 Chrontel, Inc. All Rights Reserved.
Printed in the U.S.A.
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